Multi-tier storage environments, such as two-tier storage systems, typically provide a performance tier that employs storage based on performance considerations and a capacity tier that employs storage based on capacity considerations. In this manner, multi-tier storage systems balance between the relative costs of memory and other storage and their relative speeds. Such multi-tier storage environments typically allow particular levels of performance to be achieved at a significantly lower cost than would otherwise be possible.
Metadata is additional data that describes the actual data, such as permissions for the data and where the data is stored. Although most users only care about the actual data, a common bottleneck in storage systems is often the corresponding metadata which is directly related to the number of entries in the storage system. One challenge, however, is that the amount of metadata that must be maintained can often be extremely large. A number of techniques have been proposed to improve metadata performance and/or reduce the amount of required metadata. U.S. patent application Ser. No. 14/870,968, referenced above, for example, discloses a two-tier storage system that reduces the amount of metadata to be stored in a performance tier by employing dynamically loadable namespaces (DLNs). In particular, a file system is presented as a global single namespace (SN) comprising a plurality of DLNs maintained in a capacity tier of object storage of the storage system. In response to a job submitted by an application, for example, a particular dynamically loadable namespace is dynamically loaded, including the metadata only for the particular dynamically loadable namespace, associated with the job from the capacity tier of object storage into a performance tier of storage of the storage system. Therefore, only a dynamic subset of the data in the capacity tier has metadata in the performance tier.
A need remains for methods and apparatus for filtering and/or reorganizing DLNs that are dynamically loaded into the performance tier according to metadata characteristics, such as file system attributes or user-defined extended attributes.